Inverse ice-induced moment determination on the propeller of an ice-going vessel

Abstract

This paper presents inverse methods to determine the ice-induced moment on the propeller based on shaft line torque data. The following methods are applied: Truncation of singular value decomposition (TSVD), truncation of generalized singular value decomposition (TGSVD) and Tikhonov regularization. The dynamic behavior of the structure is modeled by combining an increment form of the governing equation of torsional vibration and Newmark-β method. Inverse methods are applied on model-produced verification data and full-scale measurement data. The verification indicated that the methods are capable to solve the ice moment function in loading events where multiple consecutive ice contacts are present. Results with full-scale data were physically understandable. The three presented loading events had 1 to 4 individual ice contacts. Durations of these ice-propeller contacts were mostly 60 to 80ms. Ice contacts were observed to have a secondary peak that could be caused by a shear stress wave propagating back and forth the shaft line. After the ice contacts, the moment caused by the damping effect of water can be seen in the results.